Substantially nickel-free austenitic and corrosion resisting cr-mn-n steels



Dec. 2, 1958 E. J. DULIS ETAL 2,862,812

SUBSTANTIALLY, NICKEL-FREE AUSTENITIC AND CORROSION masrs'r-mc Cr-Mn-N'STEELS Filed m 16, 1958 3 Sheets-Sheet 2 COLD REDUCTION, PEI? cem-INVENTORS. E wA/eo dDuL/s. PETE/E R4 YSO/V. BY

ATTORNEYS.

United States Patent SUBSTANTIALLY NICKEL-FREE AUSTENITIC AND SCORRGSIONRESISTING Cr-Mn-N- STEEL Edward J. Dulis and Peter Payson, Pittsburgh,Pa., as-

signors to Crucible Steel Company of America, Pittsburgh, Pan, acorporation of New Jersey Application May 16, 1958, Serial No. 735,900

5 Claims. (Cl. 7-5125) This invention pertains to corrosion resistant,austenitic stainless steels, and more particularly to a substantiallynickel-free steel of this type, which contains as essential constituentsin addition to iron, only carbon, manganese, chromium and nitrogen, andpreferably also copper, within critically restricted ranges of each andin balanced proportions such as to impart an wholly austenitic structuretogether with excellent hot and cold forming properties as well asexcellent strength and ductility and good corrosion resistance.

This application is a continuation-in-part of our copending applicationSerial No. 651,042, filed April 5, 1957.

The past, present, and anticipated future shortage of nickel hasnecessitated steel-industry-wide efforts to develop austenitic stainlesssteels in which the nickel of the Well-known 18Cr-8Ni (A181 300 series)steels is replaced by other austenite forming and stabilizing elements,such as carbon, nitrogen, manganese, and copper. At present, two newgrades of such steels, in which nickel is partially replaced bymanganese and nitrogen have successfully passed the development stageand are now accepted as the A181 Type 201 and 202 steels, having typicalanalyses of about 6.5Mn-4.5Ni17Cr-0.25N max. 0.15C max. and9Mn5Ni-l8Cr0.25N max.-0.15C max., respectively. There has also beendeveloped the 16-16-1 type of steel, i.. e., 16Cr-16Mn-1Ni which iscompetitive with the higher nickel-bearing grades aforesaid for certainapplications. However, all such steels require substantial amounts ofnickel and hence are objectionable on this ground for reasons abovenoted.

Recently, owing to the success of the CrNiMn steels, research directedto the development of completely nickel-free Cr-Mn--N austenitic,corrosion resisting steels has been intensified. In the development of anew steel of this type, the following goals are sought: The steel shouldretain a fully austenitic structure after solution annealing at about2000" F. and rapid cooling to room temperature. Also, the retention of afully austenitic structure at normal hot Working temperatures up toabout 2300 F. is necessary because substantial amounts of delta ferritewill seriously impair the hottype of application.

workability of the steel by causing cracking and tearing during theinitial conversion into bars, rods, and strip. Also such a steel shouldhave suitable mechanical properties (strength, ductility, andWork-hardening characteristies) for successful fabrication andcommercial. utility, and also adequate corrosion resistance for theintended In addition, the steel should have good drawability,weldability, and elevated-temperature mechanical properties.

Now we have developed a steel which meets these requirements, whichrequires no nickel as an essential constituent. The steel of ourinvention is characterized in being wholly or austenitic at alltemperatures from the melting temperature down to room or atmospherictemperature. Our steel being thus free from high temperature ferrite atalltemperatures up to 2300 F., i. e., normal hot rolling temperatures,can :be easily reduced from the'ingot stage to hot bands without tearingor rupture.

Our steel can be annealed at about 2050 F. and as annealed has a yieldstrength of about 50,000 p. s. i. and a tensile strength of about145,000 p. s. i. (a ratio of about 1:3), and an elongation of about 45%.When cold reduced 30%, the steel has a yield strength of about 140,000p. s. i., a tensile strength of about 195,000 p. s. i. (a ratio of about1:1.4) and an elongation of about 15%. The steel accordingly hasexcellent cold forming properties by reason of its low yield strengthcombined with high ductility, as annealed, and by reason of its highductility after a 30% reduction. Likewise, as both annealed and coldreduced, it has adequate strength and ductility for use as a structuralmaterial in service.

Although the corrosion resistance of our steel to boiling nitric acid isnot as high as in the relatively high nickelbearing grades, such asTypes 201, 202 and 301, it is superior to that of the 16-16-1nickel-bearing steel.

The steel of the invention is, however, primarily intended as astainless type of steel for structural applications, subject primarilyto atmospheric exposure, such as for exterior and interior paneling andtrim on railway cars, automotive truck bodies, building structuresand'the like. Our tests have shown that for such applications, our newsteel has adequate corrosion resistance. In addition, it has therequisite hot and cold formability, and the requisite strength andductility both as annealed and as cold reduced, for such applications.

The broad range of analysis of our steel is:

Composition, percent Manganese ll-under 14 Chromium 14-18 Copper 0-2Silicon 0-3 Nitrogen 0.15-0.4 Carbon 0-0.15 Nitrogen plus carbon,minimum 0.075(Cr12.5)+0.1 Balance Iron Composition, Percent BroadPreferred 11-under 14- 11.5-13.5. 1446.5 14.5-15.5.

over 0.5-1.5.

The broad and preferred ranges for our typically 17Cr steel are:

Composition, Percent Broad Preferred 11-under14 11.5-13.5. 16.5-1816.5-17.5.

over 0.5-1.5. 0.15-l.5.

. 0.05-0.15. 025-04 .t 0.075 (Cr-12.5) same.

+0.1. Iron Iron.

By balance iron in our steel is meant iron except for impurities withincommercial tolerances, i. e., P and S about 0.04 max. each, and nickelabout 0.5 max.

Copper is a preferred addition to our steel in the amounts stated, as itimproves resistance of the steel to work hardening and also improves thecorrosion resistance.

As stated, the ranges and proportioning of the alloying constituents inour steel are critical for providing the desirable combination ofproperties aforesaid. For assuring an wholly austenitic structure in oursteel, we have found that the minimum carbon plus nitrogen contentshouldbe related to the chromium content as follows:'

(1) Percent (C-l-N) min.=

0.075 (percent Cr-12.5)+0.10

Although manganese over our broad range of about to under 14% helps tostabilize the austenite in the steel, beyond this range it tends to formferrite. Likewise chromium above about l7% tends to introduce a ferriticstructure.

Even with chromium and manganese thus limited, however, the steel willnot have an wholly austenitic structure in the absence of appropriateadditions of the potent austenite stabilizers carbon and nitrogen. Asshown by the above formula, derived from test results hereinafterpresented, the minimum carbon plus nitrogen, for assuring an whollyaustenitic structure, increases with the chromium content. Thus for ourtypically Cr steel, the minimum carbon plus nitrogen is about 0.27%, andfor our typically 17Cr steel the minimum carbon plus nitrogen is about0.45%. On the high side there are definite upper limits for each ofcarbon and nitrogen that can be tolerated.

High carbon produces chromium carbide precipitation in weld zones ofwelded structures made of the steel, thus depleting the chromium andlowering the corrosion resistance of the steel thereat. And since thesteel of the invention is primarily intended for applications aforesaidinvolving Welded structures, the carbon must be kept sufficiently low toassure good corrosion resistance throughout the entire structureincluding the weld zones. To this end, the carbon should not exceedabout 0.15% and preferably should be held under 0.1%.

Nitrogen is limited on the high side by the extent of its solubility inthe steel. Nitrogen present beyond the limit of solubility will evolvein gaseous form from the steel and thereby produce porous and unsoundingots. And while increasing amounts of the chromium and manganese inthe steel, increase the solubility of nitrogen therein, and thus in thisrespect, function to increase austenite formation, there are definiteupper limits beyond which an wholly austenitic structure cannot beachieved in this direction, owing to the aforesaid counteractingtendency for manganese above about 15% to produce ferrite, and the sametendency of chromium above about 17% to do so.

Our above formula for minimum carbon plus nitrogen shows, for example,that in a chromium-manganese steel containing about 18% chromium and0.1% carbon, about 0.4% nitrogen is required to impart a completelyaustenitic structure at normal hot working temperatures. We have found,however, that in order to keep 0.4% nitrogen in solution, about 15% ormore of manganese is required. But this amount of manganese in turntendsto promote the formation of delta ferrite at the hot-workingtemperatures. The alternative of increasing the carbon thereby to permitof reducing the nitrogen and man-- ganese contents, does not solve thisproblem, since it reduces the corrosion resistance of the steel at weldzones as above explained.

We accordingly set the upper limit for nitrogen at 0.4% and preferablyat 0.35%, in our steel in conjunction with the aforesaid upper broad andpreferred limits for carbon, manganese and chromium and the minimumcarbon plus nitrogen to assure the combination of good corrosionresistance and a completely austenitic structure at hot workingtemperatures and upon cooling to room temperature.

It will thus be seen that the ranges and relative proportions for eachof the essential alloying constituents, namely, carbon, manganese,chromium and nitrogen, are quite critical in our steel, and insofar aswe are aware, previously untaught in the art as to significance or as tothe novel results achieved thereby.

In the accompanying drawings to be discussed more in detail, post:

Fig. l is a phase diagram showing the relation between the minimum ofcarbon plus nitrogen versus chromium content of the steels of theinvention for maintaining an whollyaustenitic structure;

Fig. 2 illustrates graphically the variation in Rockwell C hardnessversus percent of cold reduction of representative steels of theinvention as compared to the Type 201 commercial grade;

Fig. 3 illustrates graphically the variation in tensile and yieldstrength with percent of cold reduction of representative steels of theinvention as compared to commercial steels; while Fig. 4 is a graphicalshowing of the corre- The results as In the as-cast and hot rolled-con-After a solution anneal at 2300 F., howditions, as well as after asolution anneal at 2000 and 2100 ,F., all steels, with the exception ofSteel 6971 (l5.4Cr-'0.08C0.'12N), were fully austenitic (non- F.,magnetic). and rolled into strips 3" wide and thick. {Ihecompositions ofthese steels as determined by.chemical;analysis are given in thefollowing Table I. 7

TABLE II Hardness, grain size, and austenite stability data presence ofcarbides or nitridesand delta ferrite phases in the microstructure.

ever somev steels developed delta ferrite. hot'rolled and as solutionannealed at 2300" F. are compiled in Table 11.

thick.

is As dire-experimental basislfonouri findings abovestated, a seriesofl-i-p'ound' heats of varying :C Cr-fMn N analyses were induction meltedand cast into ingots. The ingots were heated to about 2000 F., soakedone-half hour, and hammered into slabs 3%" wide and A The slabs weresurface ground, heated to 1900-1950" As pointed out above, the preferredsteels of the present invention are those in which the carbon does notexceed about 0.15% for reasons above explained. Accordingly, the steelsin Table I.having carbon of not over 0.15% -were selected for furtherinvestigation as follows:

Samples (12 x 1 x in.) of these selected steels were solution-treated at2100 F. for minutes and water quenched. The scaledsurfaces of theheat-treated samples were removed by sand blasting, and the samples ofeach steel were cold rolled to 10, and reductions in thickness. Standard'ASTM tensile test specimens (2" in gage length and-0.5" ,in-width)were-pre- 75 pared from-samples-in -the-annealed"condition and-after 10,20andj30% -cold reductions. 'The results of the de, and theSubsequently,

d M. J. Lavigne,-

#320 grit belts. Rockallographically, and de to establish the (l x 1 xin.) of all steels listed in Table 2100 and 2300 F. for 15 min- TheMagne-Gage readings were t ferrite values ,on the basis of a005413410100 0 0 .0 0.0305,... mawaammA mmammmm mmF W m warm m hw mm m mS m m .C md C na I S m mma mm mmm mmmna w a e s e mm 00% 3H3000000000003 m 1 g m m wMAL n. m c an m m m mu o m m Wm 1 1 1 r on...hi mnc m S .BHmUn 1a @r$ .1 te do o s n F 76776989790860707115466 F m mH S e e .6 e m Hf 6b 0 m w u o 11111.11111211 121111111 e. 11 e r. .L tS u m 7 P 0 3 m m mmm mmwe eo m a f. m mmmswmammmm mo wwmm m f u r O 1 76 f. re1 a w w 7 mrMa 06146768801989910421789 e nh e 1 1 I 0. 2 C .C 0MM 33333333344333344 333333 i. 1 w 1 t m m t m W HH S m S e .90. a 0 1.0 h u e n .7 uF a ma mr b m maflmamw mfimmu h mm m f m .h 8% u 0 10111n aiW C cme e 0 a0 e 1. h n I a u S f mp m t mIS tw n a. f .e.1. m. Wf ulIO a ma momm amm m wwm wwm .i h a I D w a Wot 6 g g u d m n S m a C 1 Oa n 6 p u a. uano a ea fi m m m man m m w w ah m aa m a m. n Oalaaaioizllllallltaiill n W. W t e 1% P m a o a t s 1111111111111111111111 1m 3 m p e e w S O C m Mm F T D S f. S .n r e ho as cehm pt 1w.1dm 6 D. N 99061125 76152191472312 MW h d T m m Gayest-100 22 33 4 45455 562244 e 0 n n P V T 6 ..l.mt u m M 0000 0unmouuoaodoomouooa nMccdd m l W H a a 3 t e h .1 n S .1 6 3 2 1 .1 S H yo ew su .e 1e r e oI a T n r a t X Y e r l d D. 22294465337280750808988 w 3 g a m H m W S mW n n m N w Pn a nb mt r a... nlli a qf ri a 0 00 000000000000000000000m C w 0 5 0 5 0 y 4 A: 5 5 6 WW O WMWMNMMNNUHMM$MWMMMQM RM N wmmwhmmwmwnwmm o mfialnvlfiwmfilna uuouuaauuuuauuouuauouou .6 .2 3 .stAetteiaAAjt MC 0000.0000000000000000000 6 It S n m w 5 H N MEHHMM%%%%M&%%W%%H%%%H% mmP 0 0 0 0 0 0 0 fiw0 0 0 0 0 0 0 0 nw0 nw0 0 0 fiw D 0e r I. a W 0 MM%%%%%%M%W%fi% B m 0 0 0 0 0 0 0 flwO 0 0 0 0 flm0 0 0 01 .0 1 .0 L 1H SMW d M%%M%MM%%MWM%N%WHWQUM%% l 2 O A4 5 rw5 5 6 7 -L-L- 7 0 7 7 4-A 7 -LT. m a nmwnmnnwmnumumnwmnnnmww B m 0Q0 00 0 0 0Q00 0 00000000000 A. O .1a a uauarmnn nnumwawmunncn 0 nmnw0 flm0 0 0M 0 fih0 0 0 0 flw0 0 0 0 0 00 0 W flwflnww% aw%mwm%mwwwwwfiw O LLLLLLZn MZZZZZLLZZLQMLLLL c1111.1111111111111111111 M 244 mn mmwfiqudl O 222 0011 e n C r a B.

Specimens I were heated at 2000 utes and water quenched. To producesuitable surfaces for the determination of hardness and magneticresponse, the scaled surfaces of the specimens were removed by magneticresponse of the specimens was measured by use of a Magne-Gage.

converted into percen wet grinding and finishing on well C hardnessdeterminations were ma correlation chart (T. V. Simpkinson an MetalProgress, February 1949 the specimens were prepared met microscopicexaminations were ma room temperature tensile tests are shown in TableD1 below.

The data sho'wthat an increase in the carbon plus nitrogen contentdecreases the tendency of the steel to TABLE 111 I g g Room-temperaturetensile properties l p v Gold 0.2% on ,-Tenslle nee. Steel N0. '0 N C+NCr Cu Reducset Yield Strength, .E10ng., Area, tion, Strength,1,000p.s.l.v1ercent, Percent Percent 1,000p.s.1.

a s as 2i 1 7 l 6962 0.14 0.33 0.47 17.6 20 170 20 46 30 141 191 12 37 a22 a 10 6982 0.07 0.18 0.25 14.6 0.74 20 I 90 159 30 31 30 111 201 18 489% 2% s 0 6983 0.07 0.20 0.27 14.4 1.33 l 20 m0 138 32 30 121 157 16 450 2 s2 22 22 10 5 6979 0.14 0.28 0.42 17.2 0.67 20 114 153 22 52 30 141173 14 44 O l8? s 22 10 8 4 6978 0.14 0.29 0.43 17.2 1.30 i 20 122 15023 49 30 131 171 15 42 The yield strengths of the typically 15% chromiumsteels of the above table, in the annealed condition ranged from 47,000to 50,000 p. s. i., the tensile strengths from 104,000 to 134,000 p. s.i., and the elongations from 46 to 58%. The yield strengths of thetypically 17% chromium steels in the annealed condition ranged- H from55,000 to 63,000 p. s. i., the tensile strengths fromj 109,000 to116,000 p. s. i., and the elongations from' to 59%. The results showthat an increase in the carbon plus nitrogen content tends to increasethe yield I and tensile strengths slightly, whereas additions of copper.transform to martensite during cold deformation. Also demonstrated isthe austenite-stabilizing effect of copper; that is, due to cold-workingduring the cold-rolling operation, the copper-bearing steels were lessprone to Work harden as well as to transform to martensite than thesteels that did not contain copper. For example, after 10% coldreduction Steel 6972 (no Cu) had 12% ferrite (martensite) in themicrostructure; Steel 6982 (0.74Cu) had less than 1%; and Steel 6983(1.33Cu) had none.

The average hardness increase of the 15% Cr and the 17% Cr steels uponcold rolling, together with a curve for Type 201 steel, are shown inFigure 2. On the basis of this graph, the work-hardening characteristicsof the 17% Cr steel closely resemble the characteristics of Type 201steel, whereas the 15% Cr steel shows a higher rate of work-hardening upto 10% reduction than the 17% Cr steel.

The tensile properties and work-hardening characteristics of our steelsare summarized and compared with the respective properties of knowntypes of steels in the following Table V and in Figs. 3 and 4 of thedrawings.

TABLE IV Work-hardening and transformation characteristics Composition,Percent l 2,100 F., W. Q. 10% Cold-Reduced Steel N C N G+N Cr Cu ReMagne Percent Re Magne Percent Gage Ferrite Gage Ferrite 20%Cold-Reduced 30% Cold-Reduced All steels contained 11.5-12.5% manganese,balance iron.

In Table V the values for steels according to the invention arepresented as the range of results given in the above Table IV, whereasthe values for the comparison materials were obtained from the followingsources: For U. S. Steels Cr-Mn-N steel Tenelon, from D. J. Carney,Steel, November 7, 1955, p. 138; for AISI Types 201 and 202, from R. A.Lula and W. G. Renshaw, Metal Progress, February 1956, p. 73, and E. V.Bennett, National Research Council, Materials Advisory Board Report No.MAB-4518M, June 10, 1935 (reprinted January 23, 1956); and for AISI Type301, from the above cited Metal Progress article.

copper, up to 3% silicon, 0.15 to 0.4% nitrogen, up to 0.15% carbon, theminimum carbon plus nitrogen content being related to the chromiumcontent in accordance with the following equation, percent (C+N)min.=0.075 (percent Cr-12.5 )+0.1, balance substantially iron, saidalloy being characterized by an wholly austenitic struc- .ture asquenched from 2300 F. and by good corrosion resistance to atmosphericexposure.

2. An alloy steel consisting essentially of about: 11 to under 14%manganese, 16.5 to 18% chromium, up to 2% copper, up to 3% silicon, upto 0.2% carbon, 0.25 to 0.4% nitrogen, the minimum carbon plus nitrogeni TABLE V Comparison of tensile properties Yield Tensile Percent PercentSteel Condition Strength, Strength, Elonga- Reduction 1,000p. s. 1.1,000p. s. 1. tion of Area This invention Cr {Annealed "5" 61:3 45-5835458 This invention 17 Or igigii U. S. Steel's Or-Mn-N(Tenelon).. 192lust Type 201 23 Annealed 40- 55 100-105 AISI Type 202 s ng Reduced.. 1%Annea e AISI Type 301 {30% Cold Reduced 140 170 An examination of valuesgiven in Table V and in 30 content being related to the chromium contentin ac- Figs. 3 and 4 of the drawings shows that the yield and tensilestrengths of our steels are slightly higher and the elongations slightlylower than those of the standard Type 301, 201 and 202 steels; however,the differences are not significant. Also, it is worthy of note that our17% Cr steels, in general, exhibit more favorable tensile propertiesthan the U. S. Steel experimental nickel-free, CrMn-N steel. This steelevidently corresponds to that of the U. S. Steel Corporations recentlyissued Patent 2,778,731, D. J. Carney, from Table II of which it is seenthat the steel contains substantial amounts of delta ferrite as solutionannealed at temperatures ranging from 1900 to 2300 F., this by reason ofthe high chromium content (17.520%) in conjunction with high manganese(15-20%) and low carbon plus nitrogen, as shown by the compositionsgiven in Table I of the patent.

Reverting to Figs. 3 and 4 of the drawings, it will be seen, aspreviously discussed, that the effect of adding copper to the steel ofthe invention, is to decrease the martensite transformation andwork-hardening tendencies during cold working. This behavior ismanifested by a significant lowering of the yield strength and thetensile strength and accompanying increase in tensile elongation for thecopper-bearing steels as compared to the same steel without copper.

To test the corrosion behavior of the steels of this invention in arelatively mild corrosive medium, such as is encountered in actualweathering conditions, specimens of the steels, one with copper and onewithout (Heats 6972 and 6983) were subjected to a water-vaporcolumncorrosion test in the solution-annealed (2100 F. for 15 min., waterquench) condition. The test was conducted for 10 cycles, each cycleconsisting of an 8- hour exposure to water vapor at 100 F. and of a 16-hour drying period. For comparison, specimens of the AISI Type 302 steeland of plain carbon steel were included in these tests. Visualexamination of the surfaces of the specimens after the test exposurerevealed that the steels of the invention tested showed some localizedstaining. The Type 302 specimen was apparently not affected, and theplain carbon steel was fully covered with heavy rust.

What is claimed is:

1. An alloy steel consisting essentially of about: 11 to under 14%manganese, 14 to 18% chromium, up to 2% cordance with the followingequation, percent (C+N) min.=0.075 (percent Cr--12.5)+0.1, balancesubstantially iron, said alloy being characterized by an whollyaustenitic structure as quenched from 2300 F. and by good corrosionresistance to atmospheric exposure.

3. An alloy steel consisting essentially of about: 11.5 to 13.5%manganese, 16.5 to 17.5% chromium, from more than 0.5 to 1.5% copper,from 0.15 to 1.5% silicon, from 0.05 to 0.15% carbon, from 0.25 to 0.4%nitrogen, the minimum carbon plus nitrogen content being related to thechromium content in accordance with the following equation, percent(C+N) min.=0.075 (percent Cr- 12.5)+0.1, balance substantially iron,said alloy being characterized by an wholly austenitic structure asquenched from 2300 F. and by good corrosion resistance to atmosphericexposure.

4. An alloy steel consisting essentially of about: 11 to under 14%manganese, 14 to 16.5% chromium, up to 2% copper, up to 3% silicon, upto 0.15% carbon, from 0.15 to 0.4% nitrogen, the minimum carbon plusnitrogen content being related to the chromium content in accordancewith the following equation, percent (C+N) min.=0.75 (percentCrl2.5)+0.1, balance substantially iron, said alloy being characterizedby an wholly austenitic structure as quenched from 2300 F. and by goodcorrosion resistance to atmospheric exposure.

5. An alloy steel consisting essentially of about: 11.5 to 13.5%manganese, 14.5 to 15.5% chromium, from more than 0.5 to 1.5 copper,from 0.15 to 1.5 silicon, carbon under 0.1%, from 0.25 to 0.35%nitrogen, the minimum carbon plus nitrogen content being related to thechromium content in accordance with the following equation, percent(C+N) min.=0.075 (percent Cr 12.5)+0.1, balance substantially iron, saidalloy being characterized by an wholly austenitic structure as quenchedfrom 2300 F. and by good corrosion resistance to atmospheric exposure.

References Cited in the file of this patent UNITED STATES PATENTS2,198,598 Becket et a1. Apr. 30, 1940 2,698,785 Jennings Jan. 4, 19552,789,048 De Long et al Apr. 16, 1957 FOREIGN PATENTS 152,291 AustriaIan. 25, 1938 marsh sures. PATENT OFFICE CERTIHQATE GF CGRREQTION PatentNo 2,862,812 December 2, 1958 Edward Jo Dulis et air,

It is hereby certified that error appears in the -printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 10,; line 53, for "min.=O.75" read minQ OQO'75 =0 Signed andsealed this 7th day of April 1959.

(SEAL) Attest:

KARL H, AXLINE BGBERT C. WATSON Attesting )fficcr {:ommissioner ofPatents

1. AN ALLOY STEEL CONSISTING ESSENTIALLY OF ABOUT: 11 TO UNDER 14%MANGANESE, 14 TO 18% CHROMIUM, UP TO 2% COPPER, UP TO 3% SILICON, 0.15TO 0.4% NITROGEN, UP TO 0.15% CARBON, THE MINIMUM CARBON PLUS NITROGENCONTENT BEING RELATED TO THE CHROMIUM CONTENT IN ACCORDANCE WITH THEFOLLOWING EQUATION, PERCENT (C+N) MIN=0.075 (PERCENT CR-12.5)+0.1,BALANCE SUBSTANTIALLY IRON, SAID ALLOY BEING CHARACTERIZED BY AN WHOLLYAUSTENITIC STRUCTURE AS QUENCHED FROM 2300*F. AND BY GOOD CORROSIONRESISTANCE TO ATMOSPHERIC EXPOSURE.